Recently, plural electrophotographic copying apparatuses and plural printers have been installed in one office corresponding to wide availability of personal computers. Therefore, when plural image processing apparatus are installed in an office, costs of the image processing apparatuses have been greatly studied in addition to the study of image quality of the image processing apparatuses.
When an image is formed, a monochrome image and a color image can be formed. When the monochrome image is formed, only one color material black (K) is required in either a laser scanning system or an inkjet system. On the other hand, when a color image is formed, generally, the color image is reproduced by using four color materials cyan (C), magenta (M), yellow (Y), and black (K) so that black reproducibility of the image is increased and amounts of the other color materials are reduced. In addition, when a user requests, five or more color materials including a special color material other than the CMYK materials are used.
When a color image is formed, not only may each color material be used alone, but also hue, luminance, and so on must be expressed by mixing the color materials by superposing different color material images. Therefore, in some cases, the cost of forming a color image is several times the cost of forming a monochrome image.
In order to decrease the cost of forming the color image, several studies have been performed. Generally, a color material using amount decreasing mode for decreasing a using amount of a color material, which is referred to as an economode or an ink reducing mode, is installed in an image processing apparatus.
For example, in Patent Document 1, a thinning out process is applied to image data by using a specific pattern, and the actual using amount of color materials is decreased. In Patent Document 2, the number of tones is decreased from input data with a predetermined ratio, components at a shadow side using a large amount of the color materials are decreased, and the total amount of the color materials is decreased. In Patent Document 3, a CMM (color matching method) is used and the amount of the color material is finely adjusted.
The method, in which the amount of the color materials is decreased by using CMM, is described in Patent Documents 4, 5, and 6.
In Patent Documents 4 and 6, the amount of the color materials is decreased by using CMM. In Patent Document 5, a different tone process is applied to the color materials whose luminances are different from each other in highlight and shadow by using CMM. In Patent Documents 4 through 6, when the amount of the color materials is decreased, a color region to be reproduced by image forming is decreased; however, and minimizing degradation of the color reproducibility caused by the decrease of the color region is not an objective.
That is, in Patent Documents 1 through 6, the amount of the color material is decreased or the color reproducibility in highlight and shadow is increased by using CMM. The amount of the color material to be decreased while reproducing an image in high definition and minimizing the degradation of the image quality caused by the decrease of the color material are not described. Specifically, when the amount of the color material is decreased so as not be high cost, the reproduced image is blurred, and image impression and psychological effect to be originally obtained from the color image are decreased. Consequently, cost and image quality to be satisfied by a user cannot be obtained.
[Patent Document 1] Japanese Unexamined Patent Publication No. 2006-270927
[Patent Document 2] Japanese Unexamined Patent Publication No. H09-216419
[Patent Document 3] Japanese Unexamined Patent Publication No. 2004-80266
[Patent Document 4] Japanese Unexamined Patent Publication No. 2006-68982
[Patent Document 5] PCT International Patent Application No. WOA 2003-043306
[Patent Document 6] Japanese Unexamined Patent Publication No. 2007-235661